Quadriplegic individuals demonstrate significant alterations of lung and thoracic physiology. Reduced dynamic lung compliance, abnormalities of gas transport across the lung, increased work of breathing, and restricted lung volumes all have been demonstrated in quadriplegics. Volume-pressure relationships of the total thorax, chest wall, and lungs are only partially known in this group of individuals. We will study the elastic properties of the total thorax and lungs in quadriplegic subjects and document the physiological abnormalities which occur. Thoracic and chest wall volume-pressure relationships will be determined using a sample, well tolerated, reproducible weighted spirometer technique. Static lung pressure-volume relationships will be determined using a standard interrupted deflation technique. Periodic positive pressure hyperinflation (IPPB) has been shown to alter favorably lung compliance, gas exchange and work of breathing in hyphoscoliosis. We will determine the effect of IPPB on the lung volume-pressure relationship of lungs and thorax in quadriplegics. The effects of IPPB on lung and chest wall elasticity will be studied both after prolonged use (18 weeks) and after single treatments. Additionally, the effects of IPPB on lung and thoracic tissue resistance will be studied. We will attempt to apply physiological measurements of thoracic and lung elasticity to obtain a better understanding of the total respiratory impairment in quadriplegics. Improved knowledge of the abnormal pulmonary physiology and possible improvement with IPPB will lead to an improved management of quadriplegic patients and hopefully reduce their respiratory morbidity.